Inspection method and apparatus for circuit pattern

ABSTRACT

An apparatus for measuring a sample with a circuit pattern including at least a porous low-permittivity hydrogensilsesquioxane material or a material structurally or compositionally similar to the porous low-permittivity hydrogensilsesquioxane. The apparatus includes an electron beam optics unit which enables scanning of a primary electron beam onto the sample, a detector which detects a secondary electron or a reflected electron, an image processing unit which measures a desired portion of the sample irradiated with the primary electron beam based on an output signal of the detector, and a control unit which controls the irradiation energy and density of the primary electron beam onto the sample.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/620,702, filed Jul. 17, 2003, now U.S. Pat. No. 6,952,105, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a technique for inspection of finecircuit patterns on circuit boards for semiconductor devices, liquidcrystal displays, and the like, by use of an electron beams.

As an example of the currently available processing, a typical method ofinspecting a fine circuit pattern on a wafer (board) will be described.

An integrated circuit is performed by printing patterns, which areformed on photo masks, on a wafer successively by lithography andetching. The yield of ICs produced in this way is affected by errors inthe printing patterns, the entry of foreign matters, etc; accordingly,patterns on wafers are inspected in the course of manufacture of theICs.

Defects of circuit patterns on wafers are mainly detected optically orby using an electron beam. With patterns becoming ever finer and morecomplex, the shapes becoming ever more complex, and the materialsbecoming more diversified, it has become more difficult to detectdefects by use of optical methods. Under the circumstances, there havebeen proposed various methods of inspecting such patterns on the basisof their images as reproduced with electron beams, the resolution ofwhich images is higher than that of optical images.

According to some methods that have been proposed, an electron beam isapplied to a circuit board to obtain an image of its circuit pattern.When defects are detected, the images are stored and analyzed todetermine the kinds of defects automatically (for example, see JP-A No.160402/1999, referred to hereinafter as Patent Document 1).

As an example, a typical existing method of measuring the dimensions ofa fine circuit pattern on a wafer will be described. As the circuitpatterns of IC's become finer, more strict control of the dimensions andshapes of the circuit patterns on the wafers is required. In thisregard, even slight dimensional errors affect the performance of theICs.

Circuit patterns on wafers are measured optically or by using anelectron beam. Electron beams are mainly used for the measurement ofholes and the measurement of two-dimensional images. According to somemethods that have been proposed, the top surface of the sample underinspection is charged with an electron beam and a first accelerationvoltage, and then a second acceleration voltage is applied to the sampleto obtain an image for observation (for example, see Patent Document 2:JP-A No. 200579/2000, referred to hereinafter as Patent Document 2).

As described above, with use of the technique for inspecting andmeasuring circuit patterns with electron beams, the quality control,such as the control of dimensions and the detection of defects, under ahigher lateral resolution is possible.

The existing inspection apparatuses use a probe current of several tensof nanoamperes and an electron beam that is accelerated in the rangefrom several hundred volts to ten kilovolts, which poses no problems solong as silicon oxide or the like is used for the insulating filmsbetween layers. With circuit patterns ever becoming finer and thedata-processing speeds of ICs ever increasing, however, it is becomingessential to use porous low-permittivity materials.

Although Patent Documents 1 and 2 claim that the acceleration voltage ofan electron beam against a wafer is variable in the range from severalhundred volts to ten kilovolts (in the case of an inspection apparatus)and several tens of volts to two kilovolts (in the case of alength-measuring apparatus), they do not mention any technique forinspection and measurement that is capable of reducing damage to resistsand porous low-permittivity materials.

As described above, the prior methods hardly address the problem ofdamage to circuit patterns that is caused by the exposure of thematerials thereof to electron beams. Accordingly, when wafers withcircuit patterns including resists and porous materials are inspected,the resists and porous materials are damaged and the dimensions ofcircuit patterns deviate from their design values.

The present inventor et al. have ascertained that when wafers includingresists and porous materials are inspected by the existing methods, thefollowing damage occurs to wafers.

-   (1) Materials are decomposed and shrink. Patterns on wafers change    under the exposure to electron beams, and the reliability of    measurement is reduced.-   (2) Materials are decomposed by exposure to electron beams, which    affects their characteristics, such as adhesion to other materials.

The above-described phenomena (1) and (2) lower the yield and theperformance of ICs.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a technique that iscapable of reducing damage, including shrinkage, to resists and porouslow-permittivity materials that are included in fine patterns on wafers,while they are being inspected with an electron beam.

The foregoing object of the present invention can be achieved byoptimizing the irradiation energy of an electron beam and limiting itsirradiation density.

According to a study by the present inventor et al., the damage, such asshrinkage and spoilage, to a resist or porous low-permittivity materialin a circuit board, which is caused by an electron beam, largely dependson the acceleration voltage of the electron beam relative to the boardand the incident density of the beam into the board. The presentinventor took porous low-permittivity materials (for example, porouslow-permittivity hydrogensilsesquioxane (HSQ) materials) as examples andstudied their shrinkage due to exposure to an electron beam; and, it wasfound that, as the irradiation energy of the electron beam increased,the shrinkage increased, indicating a strong dependency on irradiationenergy, and that the shrinkage tended to saturate as the irradiationdensity of an electron beam increased. Thus, the present invention isbased on the new knowledge that the irradiation energy and density of anelectron beam govern the damage to porous materials.

The present inventor et al. studied the shrinkage of the above-mentionedporous low-permittivity materials under conditions of changing probecurrent and changing irradiation density of an electron beam, and it wasfound that the shrinkage hardly changed while the irradiation densitywas kept constant and the probe current was increased 5,000 times withinthe range of the study. Thus, the present inventor et al. havedetermined that the damage to a circuit pattern due to exposure to aprimary electron beam could be reduced to an allowable range, regardlessof the probe current of the beam, by controlling the irradiation energyand density of the beam.

The damage to a porous material due to exposure to an electron beam iscaused by direct action between incident electrons and bonding electronsin the material, or by thermal decomposition due to incident energywhich raises the surface temperature of the sample. The present inventoret al. found that the former cause was predominant over the latter one,while the probe current of the electron beam was kept constant.

The lower the irradiation energy of the primary electron beam is, theshallower the incidence of the beam is and thus the smaller the area ofdamage due to exposure to the beam is. Besides, the efficiency ofdestruction by an incident electron beam can be considered dependent onthe irradiation energy of the beam.

Accordingly, damage, such as shrinkage and spoilage to resists andporous low-permittivity materials during inspection and lengthmeasuring, can be reduced by reducing the irradiation energy and densityof the primary electron beam. The control of the irradiation density ofan electron beam can be accomplished by adjusting the probe current, thescanning area, the scanning speed, and the number of times of scanningby the beam.

Now a typical configuration, which may be used to carry out the methodfor inspecting circuit patterns according to the present invention, willbe described.

(1) According to the invention, there is provided a method of inspectinga board with a circuit pattern including at least a porouslow-permittivity material (for example, a porous low-permittivityhydrogensilsesquioxane material), or a material similar to it in termsof structure or composition. The method comprises a step of scanning thecircuit pattern with a primary electron beam; a step of detectingsecondary electrons generated, or the electrons reflected from the boarddue to the irradiation, or both the former and latter electrons, andconverting the electrons into signals; and a step of transforming thesignals into an image, displaying the image, and inspecting the circuitpattern. Damage, including shrinkage, to the circuit pattern by theprimary electron beam is reduced by controlling the irradiation energyand density of the primary electron beam.

(2) According to the invention, there is provided the method of theabove paragraph (1), wherein the shrinkage of the circuit pattern due toexposure to the primary electron beam is reduced to 2.4 nm or less bysetting the irradiation energy of the primary electron beam to 300 eV orless.

(3) According to the invention, there is provided the method of theabove paragraph (1), wherein the irradiation density of the primaryelectron beam is limited according to the irradiation energy of theprimary electron beam and depending on the kind of said low-permittivitymaterial or said similar material.

(4) According to the invention, there is provided the method of theabove paragraph (1), which further comprises a step of recording theirradiation history of the board, such as the irradiation energy, theprobe current, and the irradiation density of the primary electron beamand the areas of the circuit pattern to be exposed to the primaryelectron beam.

(5) According to the invention, there is provided the method of theabove paragraph (1), which further comprises a step of finding, inadvance, for each material included in the board, the correlationsbetween (i) parameters including the irradiation energy, probe current,and irradiation density of the primary electron beam, and (ii)dimensional changes of the circuit pattern; and

a step of adjusting at least one of the parameters before the circuitpattern is scanned with the primary electron beam.

(6) According to the invention, there is provided the method of theabove paragraph (1), wherein the irradiation density of the primaryelectron beam is controlled by (i) calculating, in advance, the maximumdose of irradiation per unit area in each area of the circuit pattern tobe exposed to the primary electron beam, and (ii) limiting theirradiation density of the primary electron beam to a value below themaximum dose of irradiation in said area during the inspection of theboard.

(7) According to the invention, there is provided a method of inspectinga board with a circuit pattern including at least a porouslow-permittivity material (for example, a porous low-permittivityhydrogensilsesquioxane material), or a material similar to it in termsof structure or composition. The method comprises a step of scanning thecircuit pattern with a primary electron beam; a step of detecting thesecondary electrons generated, or the electrons reflected from the boarddue to the irradiation, or both the former and latter electrons, andconverting the electrons into signals; and a step of transforming thesignals into an image, displaying the image, and inspecting the circuitpattern. The shrinkage of the circuit pattern due to the exposure to theprimary electron beam is reduced to 2.4 nm or less by setting theirradiation energy of the primary electron beam to 300 eV or less.

(8) According to the invention, there is provided a method of inspectinga board with a circuit pattern including at least a porouslow-permittivity material (for example, a porous low-permittivityhydrogensilsesquioxane material), or a material similar to it in termsof structure or composition. The method comprises a step of scanning thecircuit pattern with a primary electron beam; a step of detecting thesecondary electrons generated, or the electrons reflected from the boarddue to the irradiation, or both the former and latter electrons, andconverting the electrons into signals; and a step of transforming thesignals into an image, displaying the image, and inspecting the circuitpattern. The shrinkage of the circuit pattern due to the exposure to theprimary electron beam is reduced to 2.4 nm or less by (i) setting theirradiation energy of the primary electron beam to 300 eV or less, or(ii) setting the irradiation density of the primary electron beam to 1.4C/m², if the irradiation energy of the primary electron beam is about800 eV or more.

(9) According to the invention, there is provided an apparatus forinspecting a board with a circuit pattern. At least the areas of thecircuit pattern to be exposed to a primary electron beam include atleast a porous low-permittivity material (for example, a porouslow-permittivity hydrogensilsesquioxane material), or a material similarto it in terms of structure or composition. The apparatus comprises ameans for scanning the circuit pattern with the primary electron beam; ameans for detecting the secondary electrons generated, or the electronsreflected from the board due to the irradiation, or both the former andlatter electrons, and converting the electrons into signals; and a meansfor transforming the signals into an image, displaying the image, andinspecting the circuit pattern. Damage, including shrinkage, to thecircuit pattern by the primary electron beam is reduced by controllingthe irradiation energy and density of the primary electron beam.Besides, the shrinkage of the circuit pattern due to the exposure to theprimary electron beam is reduced to 2.4 nm or less by setting theirradiation energy of the primary electron beam to 300 eV or less.

-   -   (10) According to the invention, there is provided a method of        inspecting a semiconductor device with a primary electron beam.        The method comprises a step of scanning the circuit pattern of        the board of the semiconductor device with the primary electron        beam; a step of detecting the secondary electrons generated, or        the electrons reflected from the board due to the irradiation,        or both the former and latter electrons and converting the        electrons into signals; and a step of transforming the signals        into an image and displaying the image. Before the fine circuit        pattern of the integrated circuit is inspected with the primary        electron beam, (i) the various conditions (including the        irradiation energy and the probe current of the beam, and the        magnifying power for observation) of irradiation are set, (ii)        the materials included in the circuit pattern are identified,        and (iii) the allowable level of damage to the materials is set.        Then, the maximum irradiation density to each inspection area of        the circuit pattern is controlled on the basis of data on the        correlations between (i) the irradiation conditions and the        allowable damage level.

The above data are quantitative ones on the correlations between (i) thechange of damage to a resist or porous low-permittivity material and(ii) the irradiation energy, the probe current, and irradiation densityof the primary electron beam.

Preferably, included in the method of the above paragraph (10) are astep of registering the data on correlations and a step of providing anoptimal number of times of irradiation.

(11) According to the invention, there is provided a method ofinspecting a semiconductor device with a primary electron beam. Themethod comprises a step of scanning the circuit pattern of the board ofthe semiconductor device with the primary electron beam; a step ofdetecting the secondary electrons generated, or the electrons reflectedfrom the board due to the irradiation, or both the former and latterelectrons, and converting the electrons into signals; and a step oftransforming the signals into an image and displaying the image. Theintegrated-circuit board includes at least a porous low-permittivityhydrogensilsesquioxane material, or a material similar to it in terms ofstructure or composition. The shrinkage of the circuit pattern due tothe exposure to the primary electron beam is reduced to 2.4 nm or lessby (i) setting the irradiation energy of the primary electron beam to300 eV or less, or (ii) setting the irradiation density of the primaryelectron beam to 1.4 C/m² or less, if the irradiation energy of theprimary electron beam is about 800 eV or more.

(12) According to the invention, there is provided a method ofinspecting a semiconductor device with a primary electron beam. Themethod comprises a step of scanning the circuit pattern of the board ofthe semiconductor device with the primary electron beam; a step ofdetecting the secondary electrons generated, or the electrons reflectedfrom the board due to the irradiation, or both the former and latterelectrons, and converting the electrons into signals; and a step oftransforming the signals into an image and displaying the image. Themethod further comprises a step of (i) loading the integrated-circuitboard, (ii) displaying a picture to set the conditions of inspection tobe outputted, (iii) inputting parameters including the kind of theresist or low-permittivity material included in the board, theirradiation energy and probe current of the primary electron beam usedin the inspection, and the magnifying power for observation, (iv)displaying the maximum number of times of irradiation at an inspectionarea on the circuit pattern, and (v) setting the actual number of timesof irradiation.

The inspection technique of the present invention has the followingadvantages over presently available methods and apparatus.

(1) By setting the rated irradiation energy of a primary electron beamto 20–500 eV for porous materials, the damage can be reduced to such adegree that the damage can be ignored even in the case ofintegrated-circuit boards with nodes of 100 nm or less. Accordingly,integrated-circuit boards comprising materials that are unstable underirradiation, such as porous materials, can be inspected without damagingthem, which the existing inspection apparatus (their irradiation energyis over 300 eV) are not capable of.

(2) Because the irradiation energy is low, only signals of secondaryelectrons being emitted and electrons that are reflected from thesurface of a sample are detected, without the results being affected bysecondary electrons being emitted or electrons that are reflected frombelow the surface. Thus, the dimensions and shapes of circuit patternscan be inspected with a higher precision.

With the technique of the present invention, the electro-optical systemand other systems of an inspection apparatus are designed so that anoptimal performance (for example, the diameter of the electron beam isminimized) can be derived with an irradiation energy of 300 eV. Thus,measurement and observation with a higher precision can be realized.

The rated irradiation energy of the existing methods of inspectingcircuit patterns with an electron beam is 500 eV or more (includinglength measurement). If a porous material is exposed to an electron beamof typical irradiation density, a shrinkage of 10 nm or so occurs. Withthe technique of the present invention, however, the shrinkage of porousmaterials can be reduced to 1–2 nm by setting the irradiation energy ofan electron beam to 300 eV or limiting the irradiation density of thebeam. Thus, with the technique of the present invention,integrated-circuit boards, which include porous materials, and of whichthe nodes are 100 nm or less, can be inspected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a retarding-type scanning inspectionapparatus using electron-beam irradiation according to the presentinvention;

FIG. 2 is a flowchart of the processing performed according to a firstembodiment of the present invention;

FIG. 3 is a flowchart of the processing performed according to a secondembodiment of the present invention;

FIG. 4 is a block diagram of a third embodiment of the presentinvention;

FIG. 5A is a microscopic image which shows the shrinkage of a XLK film,to which an electron beam was applied by using the apparatus of FIG. 1and the existing electron-beam method of inspecting circuit patterns;

FIGS. 5B and 5C are microscopic images which show the shrinkage of XLKfilm, to which an electron beam was applied by using the same apparatusand methods of inspecting circuit patterns according to the presentinvention;

FIG. 6A is a diagram showing a cross section of a porouslow-permittivity material before an electron beam is applied by theexisting method;

FIG. 6B is a diagram showing a cross section of the porouslow-permittivity material to which an electron beam was applied by theexisting method;

FIG. 6C is a diagram which shows the shrinkage of the porouslow-permittivity material to which an electron beam was applied by aconventional method;

FIG. 6D is a diagram which shows a cross section of the same porouslow-permittivity material to which an electron beam was applied by themethod of the present invention;

FIG. 7 is a graph which shows variations in shrinkage of a filmaccording to the inspection method of the present invention and aconventional inspection method; and

FIG. 8 is a diagram which illustrates an example of a specificationscreen of GUI command level functions in forming a recipe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, various embodiments of a method and apparatusfor inspecting circuit patterns in accordance with the present inventionwill be described in detail.

First Embodiment

FIG. 1 is a schematic illustration of a typical retarding-type scanninginspection apparatus which uses electron-beam irradiation. The object ofthe present invention is to control the integrated number of times ofirradiation of a primary electron beam at each inspection area of acircuit pattern, based on the irradiation energy and probe current ofthe beam, the magnifying power for observation, and the scanning rateemployed during inspection, depending on the kinds of resists or thekinds of porous, low-permittivity materials present in the circuitpattern, in order to prevent or reduce the damage to circuit patterns byirradiation of the primary electron beam.

The irradiation energy directed toward a semiconductor device (or anintegrated-circuit board) under inspection can be changed by theordinary method of changing the acceleration voltage of electronsemitted from the electron gun. In accordance with the present invention,however, embodiments which involve the use of a retarding-typeinspection apparatus employing electron-beam irradiation will bedescribed.

When an extraction voltage 3 is applied between a field-emission cathode1 and an extractor 2, electrons 4 are emitted. Emitted electrons 4 areaccelerated (or decelerated) between the extractor 2 and an anode 5,which is at ground potential. The acceleration voltage of the resultingelectron beam (primary electron beam) 7, formed of electrons which havepassed the anode 5, corresponds to the accelerating voltage of theelectron gun.

The primary electron beam 7, which is accelerated by the anode 5,undergoes scanning deflection by a condenser lens 14 and a scanningdeflector 15. The deflecting intensity of the scanning deflector 15 isvaried to produce two-dimensional scanning of the top surface of asample 12 with the focus at the center of an objective lens 16. Thedeflected primary electron beam 7 is accelerated by a post-deflectionacceleration voltage 21 applied by an accelerating cylinder 9 that isprovided in a passage of the objective lens 16. The primary electronbeam 7, after the post-deflection acceleration, is focused on the sample12 by the objective lens 16. A generator 13 generates a negativeretarding voltage, which is applied to the sample 12 to form adeceleration field between the objective lens 16 and the sample 12.After passing through the objective lens 16, the primary electron beam 7is decelerated by the deceleration field and reaches the sample 12.

With the configuration described above, the acceleration voltage of theprimary electron beam 7, at the time that it passes through theobjective lens 16, is the sum of the acceleration voltage 6 of theelectron gun and the post-deflection acceleration voltage 21, which ishigher than the acceleration voltage at the time of incidence of thebeam 7 into the sample 12 (the acceleration voltage 6 of the electrongun minus the retarding voltage 13). Accordingly, a finer electron beam(high spatial resolution) is obtained, compared with the primaryelectron beam 7 that is focused by the objective lens 16 under theacceleration voltage at the time of incidence of the beam 7 into thesample 12. This is accomplished by a reduced chromatic aberration of theobjective lens 16. If the acceleration voltage 6 of the electron gun is10 kV, the post-deflection acceleration voltage 21 is 8 kV, and theretarding voltage is 9.7 kV, the primary electron beam 7 passes throughthe objective lens 16 under an acceleration voltage of 18 kV, and theirradiation energy of the primary electron beam 7 at the time ofincidence is 300 eV. The spatial resolution in this example is about 2.5nm, whereas the resolution is 10 nm, if the primary electron beam 7 withirradiation energy of 1 keV is focused by the objective lens 16.

To accomplish damage-free inspection of resists or porous-typematerials, the irradiation energy has to be reduced to 300 eV or less,or the irradiation density has to be limited. A high spatial resolutionof, for example, 3 nm or less, with an irradiation energy of 300 eV, canbe obtained with the above setting.

When the primary electron beam 7 is applied to the sample 12, secondarysignals 22 are generated. The secondary signals 22 to be used consist ofsecondary electrons and reflected electrons. The electric field formedbetween the objective lens 16 and the sample 12 acts on the secondarysignals 22 as an acceleration field; therefore, the secondary signals 22are attracted into the passage of the objective lens 16 and rise throughthe passage under the action of the objective 16. After passing throughthe passage, the secondary signals 22 pass through the ExB deflector 11and collide with a reflector 27. The reflector 27 is a conductive plate,and it has an opening in its center to let the primary electron beam 7pass there-through. The collision surface of the reflector 27 is coatedwith a material that is highly generative of secondary electrons, suchas gold. This material is coated on the surface of the reflector 27 bythe vapor deposition method. The secondary electrons and reflectedelectrons of secondary signals 22 collide with the reflector 27 throughalmost the same path.

The secondary and reflected electrons of secondary signals 22 collidewith the reflector 27 to generate secondary electrons 28, which aredetected and converted into electrical signals by a secondary-electrondetector 25 and are amplified by a preamplifier 31. A monitor 23undergoes brilliance modulation in response to the output signals of thepreamplifier 31 to produce a two-dimensional image that is synchronouswith the primary electron beam 7. Alternatively, the output signals ofthe preamplifier 31 may be converted into digital signals by ananalog-digital converter 32, after which the digital signals are sentthrough a buffer 33 to an image storage 34 or 35. The secondary-electrondetector 25 may be a semiconductor detector or an MCP (micro-channelplate). The images stored in the image storages 34 and 35 are sentthrough an image processor 36 to a defect detector 37, where the kindsand locations of defects are determined and recorded.

If the irradiation energy of the primary electron beam 7 is reduced to,for example, 300 eV or less, the control of electrification of the topsurface of the sample 12 becomes more difficult. To cope with thisproblem, an electrification-controlling electrode 17 is provided betweenthe objective lens 16 and the sample 12. A power supply 24 applies anappropriate voltage to the electrification-controlling electrode 17 toform an appropriate electric field between the objective lens 16 and thesample 12, thereby to control the quantity of the secondary signals 22returning to the sample 12. Thus, the electrification potential of thetop surface of the sample 12 can be precisely controlled.

The output signals of the secondary-electron detector 25 aresynchronized with the scan signals of the primary electron beam 7, whichare used to display an image on an electron-beam scan image display andstore the image in the data-processing unit 26, including the storages.The data-processing unit 26 processes the image and determines andrecords the shapes and dimensions of the image.

An aperture diaphragm 8 is provided to control the opening angle of theprimary electron beam 7, and an adjusting knob 10 is provided to alignthe aperture diaphragm 8 with the vertical center axis of the inspectionapparatus. The reference numeral 18 indicates a mechanism for moving thesample 12 in the X and Y directions. An insulating plate 20 is providedon the mechanism 18. On the insulating plate 20, there is a sampleholder 19, to which the retarding voltage 13 is applied. When a sample12 is placed on the sample holder 19, the retarding voltage 13 isapplied to the sample 12, as well. The reference numeral 29 indicates ablanker. By applying a blanking voltage 30 to the blanker 29, theprimary electron beam 7 is deflected for collision with the aperturediaphragm 8; accordingly, when this occurs, the primary electron beam 7can be controlled so as to be prevented from reaching the sample 12.Thus, the primary electron beam 7 is applied to the sample 12 onlyduring the observation and irradiation of the sample 12. For example,while the conditions of irradiation are calculated and set, the primaryelectron beam 7 is prevented from reaching the sample 12; and, hence,the irradiation density of the primary electron beam 7 can precisely becontrolled.

Referring to the flowchart of FIG. 2, a damage-free method of inspectingporous, low-permittivity materials according to the present embodimentwill be described.

Referring to a database, the kind of a resist or low-permittivitymaterial included in an integrated-circuit board is designated (Step42), and then an irradiation energy capable of damage-free inspection(Step 43) is selected. The electro-optical system is adjusted with theselected irradiation energy (Step 44). Referring to the optical orelectron-beam scan image of the circuit pattern, an inspection area andthe magnitude of the probe current of the electron beam to be used forinspection are specified, and the magnifying power for observation ofthe area is determined (Step 45).

In Step 45, the image (image “A”) is stored in a storage, if necessary.

Thereafter, the primary electron beam 7 is interrupted using the blanker29 (Step 46); and, the maximum number of times of irradiation isestimated at each inspection area, and the locations of irradiation andthe maximum number of times of irradiation are stored in a storage (Step47).

If the estimated number of times of irradiation is smaller than theminimum number of times of irradiation required to obtain an SEM(scanning electron microscope) image with a sufficient signal-to-noiseratio, the measurement is deemed to be impossible (Step 48). In thiscase, the system returns to Step 45 to specify an inspection area, probecurrent, and magnifying power again, and Steps 44–48 are repeated. Ifthe measurement is possible in Step 48, the system advances to Step 49;wherein, if it is necessary to change the irradiation energy, the systemreturns to Step 43 and Steps 43–49 are repeated.

If it is not necessary to change the irradiation energy in Step 49, itis determined whether a charging process to raise the yield of secondarysignals is necessary (Step 50). If the processing is not necessary, theblanker 29 is turned off (Step 55), the inspection area is measured atthe specified magnifying power (image “B”) (Step 56), and the result isreported (Step 57).

If a primary electron beam 7 with higher irradiation energy is appliedto a sample 12 for higher spatial resolution, the irradiation density ofthe beam 7 is limited so as to reduce damage to the sample 12.

If the top surface of the sample 12 has to be charged before inspection,the primary electron beam 7 is set to an appropriate level ofirradiation energy, and the charging process is carried out (Steps51–53).

The irradiation density values of all of the spots of the inspectionarea are added up, and the measuring time is set so that the irradiationwill not exceed its upper limit.

The dimensions and shapes of the circuit pattern are measured andchecked on the image “B.” If the inspection apparatus is automaticallyoperated, data on the inspection area and conditions of inspection maybe read from a database without manual observation, and an image “B” ofthe inspection area may be directly recorded. The results of measurementand checkups of dimensions and shapes on the image “B” are compared withdata in the database for judgment.

Thereafter, the system moves to another inspection area, and theabove-described process is repeated. The above-described process isstored as a program in the system, and the program is executed.

Second Embodiment

Referring the flowchart of FIG. 3, a second embodiment of thedamage-free inspection method according to the present invention will bedescribed. Since the configuration of the inspection apparatus for thissecond embodiment is the same as that for the first embodiment, arepeated description of the apparatus will be omitted here.

The shrinkage of porous low-permittivity HSQ materials under irradiationtends to saturate as the irradiation density of the primary electronbeam increases. If the irradiation energy of the primary electron beamis sufficiently low, monitoring of the irradiation density of theprimary electron beam during inspection is unnecessary, so long as theeffects on the performance and yield of the integrated-circuit boardsare at such an insubstantial level that they can be ignored if theshrinkage of a porous material becomes steady.

In this embodiment, by designating the kind of porous material includedin the sample 12 (Step 58), such damage-free irradiation energy isprovided (Step 59). Thereafter, as in the case of the first embodiment,the electro-optical system is adjusted with the selected damage-freeirradiation energy (Step 60), and while looking at the scan image of thesample, the operator marks an inspection area and determines themagnifying power for the observation of the area (Step 61).

Then, the dimensions and shapes of the circuit pattern in the inspectionarea are manually or automatically measured and checked and the resultsare stored. As in the case of the first embodiment, if the top surfaceof the sample 12 has to be charged before measurement, the chargingprocess is carried out (Step 63–65).

Third Embodiment

Referring to FIG. 4, a third embodiment of the method of inspecting acircuit pattern of an integrated-circuit board, including a resist or aporous material, will be described. The inspection apparatus used inthis third embodiment is similar to that used in the first embodiment,and it is represented by the sections surrounded by the broken line ofFIG. 4. The reference numerals 71, 72, and 73 are a control system, abody tube, and a wafer chamber including a stage, respectively.

Data including information on the inspection areas of the circuitpattern at a manufacturing step are read in advance into the measuringapparatus from another storage 70, including a database of the circuitpatterns of the manufacturing steps of the integrated-circuit board.When an inspection area of the circuit pattern is selected from thedata, the measuring apparatus directly generates an electron-beam scanimage of the inspection area and measures the dimensions and shapes ofthe circuit pattern on the image. Thus, irradiation can be confined toinspection areas; and, hence, the damage to the board due to theinspection can be minimized. The process of inspection is similar to themethods employed in the first and second embodiments (FIGS. 2 and 3). Asto the information on inspection areas of the circuit patterns ofmanufacturing steps of the integrated-circuit board, data obtained byother measuring apparatuses may be read into the above-describedmeasuring apparatus.

FIG. 5A shows the shrinkage of a XLK film to which an electron beam wasapplied by using the apparatus of FIG. 1, using the existingelectron-beam method of inspecting circuit patterns. FIGS. 5B and 5Cshow the shrinkage of a XLK film to which an electron beam was appliedby using the same apparatus, but this time with methods of inspectingcircuit patterns according to the present invention. The measurementsshown in those figures were taken with an AFM (atomic force microscope).

The irradiation density is the same (17.7 C/cm²) in the three cases. Theshrinkage was about 5 nm in the case of the existing method (theirradiation energy was 800 eV) as shown in FIG. 5A; whereas, theshrinkage hardly occurred in the cases of the methods of the presentinvention (the irradiation energy was 300 eV and 200 eV, respectively),as shown in FIGS. 5B and 5C. Thus, the methods of the present inventionproved to be capable of reducing damage, such as dimensional variationof circuit patterns, due to an inspection in which an electron beam isused.

FIGS. 6A to 6C are directed to an observation of a cross-sectionalprofile of a sidewall of a bare hole, the sidewall being made of alow-permittivity material. The observation was made by an SEM (with lowirradiation energy) before and after applying an electron beam to awafer including a low-permittivity material as an inter-layer insulatorfilm in its circuit pattern (bare hole), using the apparatus of FIG. 1and the existing electron-beam method of inspecting circuit patterns.When an electron beam was applied by the existing method (irradiationenergy was 800 eV) to the profile of the sidewall before the electronbeam irradiation (FIG. 6A), a primary electron beam or a secondarysignal therefrom enters the low-permittivity material of the sidewall(FIG. 6B), causing the material to shrink (FIG. 6C).

On the other hand, when the measuring method of the present invention isused in the device of the first embodiment, shrinkage was hardlyobserved after the inspection of the same pattern (FIG. 6D).

FIG. 7 shows, for each value of irradiation energy of the primaryelectron beam, the shrinkage of a porous HSQ film according to thechange in irradiation density. It can be seen that the shrinkage of thefilm largely depends on the irradiation energy of the primary electronbeam and tends to saturate as the irradiation density of the electronbeam increases.

When an irradiation energy of 1,000 eV was applied to the porous HSQfilm by the existing electron beam inspection method, at typicalirradiation density “a,” the shrinkage of the film was “b.” On the otherhand, when the measuring method of the present invention was used in thedevice of the first embodiment, since the allowable level “d” ofshrinkage was set in advance, the inspection could be executed in such away that the shrinkage of the film due to the inspection did not exceed“d” the irradiation density was “c” or lower. Further, the shrinkage ofthe film due to the inspection was reduced to “d” or less by setting theirradiation energy of the primary electron beam to 500 eV and 300 eV.

As an example of the inspection method according to the presentinvention, FIG. 8 shows a specification screen of GUI (Graphical UserInterface) command level functions for setting the inspecting conditionswhen forming a recipe. On this screen, the names of parts and theirfunctions are as follows.

(1) Component Box for selecting the kind of resist/low-permittivitymaterial: Select the name of a resist/low-permittivity material to behit by the electron beam on the semiconductor device to be inspectedfrom among items in the component box.

(2) Component Box for selecting the shrinkage allowable level: Selectthe maximum value of shrinkage due to electron beam irradiation fromamong items in the component box in accordance with the specification ofa semiconductor device.

(3) Component Box for selecting the electron-beam irradiation energy:Select the irradiation energy of the primary electron beam used in theinspection from among items in the component box.

(4) Component Box for selecting the magnifying power for observation:Select a scanning range (magnifying power for observation) of theprimary electron beam in the inspection from among items in thecomponent box.

(5) Component Box for selecting the probe current: Select the probecurrent value of the primary electron beam used in the inspection fromamong items in the component box.

(6) Set Button: When this button is pressed, inputted data in Steps(1)–(5) become effective, and the component box on the right forselecting the number of frames to be irradiated is enabled.

(7) Component Box for selecting the number of frames to be irradiated:Out of items in the component box, select the number of times ofirradiation to each inspection area under inspection from among theavailable numbers of frames to be irradiated that are calculated in Step(6).

(8) OK Button: When this button is pressed, the inputted data in Step(7) becomes effective.

(9) Form Recipe Button: When this button is pressed, a screen forforming a recipe for the inspection is generated and displayed.

(10) Clear Button: When this button is pressed, the inputted data inSteps (1)–(5) are cleared and a reentrant procedure becomes possible.

(11) Cancel Button: When this button is pressed, even if the OK button(8) has already been pressed the inputted data in Step (7) is abandoned,and reselection becomes possible.

(12) OK Button: When this button is pressed, the contents that have beenset in the regions A and B become effective, and the system goes to thenext step of the recipe formation.

(13) Cancel Button: When this button is pressed, all the data inputtedin the regions A and B are abandoned, which makes it possible to inputconditions from scratch.

Action/processing and the contents of the processing are as follows:

1) Construction of recipe forming screen (9).

Contents of Processing: (a) Generate a screen, and (b) Enable region Aof the screen for inputting conditions.

2) Input of inspecting conditions (1)–(6).

Contents of Processing: (a) Select the kind of resist orlow-permittivity material in the semiconductor device, the allowablelevel for shrinkage of materials caused by the electron beamirradiation, the irradiation energy and probe current of the primaryelectron beam, and the magnifying power for scanning during theinspection. (b) Read data on the correlation between the conditions ofirradiation of the electron beam stored in the device in advance and theshrinkage of the material to be inspected, calculate the number offrames in which the same inspection area can be irradiated during theinspection, and store such data in the storage. (c) Disable region A andenable region B.

3) Input the number of frames in which the same inspection area can beirradiated during inspection, (7)–(8), and (12).

Contents of Processing: (a) Input the number of irradiation framescalculated in Step 2) which are usable in the inspection. (b) Put awaythe screen for inputting conditions, and generate/display the nextsetting screen necessary for the inspection.

As described above in detail, according to the present invention, withrespect to objects which have not been capable of measurement, such as apattern on a semiconductor device including porous low-permittivitymaterials, such as an ArF resist material, a porous low-permittivityhydrogensilsesquioxane (HSQ) material and the like, damage-free ordamage-reducing measurement in measuring the dimensions and shapes,detecting defects and reviewing features becomes possible. Thus, thedamage to the semiconductor device due to the inspection itself can beminimized, information closer to the actual state of the semiconductordevice can be obtained, and the inspection can be performed with higherprecision and reliability by using an electron beam of low accelerationvoltage.

1. An apparatus for measuring a sample with a pattern, comprising: anelectron beam optics unit which scans a primary electron beam onto thesample; a detector which detects a secondary electron, or a reflectedelectron; a data processing unit which executes measurement of a desiredportion of the sample; a control unit to control the electron beamoptics unit; and storage means for storing correlation data betweeninformation of damage level permissible to the sample and an irradiationcondition including irradiation energy, probe current, and irradiationdensity of the primary electron beam; wherein the control unitdetermines the maximum irradiation density of the primary electron beambased on the information, and the control unit controls the irradiationdensity in accordance with the determined maximum irradiation density.2. An apparatus according to claim 1, wherein the apparatus enablesmeasurement of a dimension of the pattern with a shrinkage of no morethan 2.4 nm.
 3. An apparatus according to claim 1, wherein the controlunit limits the irradiation density of the primary electron beam basedon the irradiation energy of the primary electron beam and the kind ofthe low-permittivity material.
 4. An apparatus according to claim 1,further comprising an input unit for setting inspecting conditionsbefore inspection or during inspection.
 5. An apparatus according toclaim 4, wherein the inspecting conditions include at least an item ofspecifying materials and magnifying power for observation.
 6. Anapparatus according to claim 4, further comprising a storing unit forstoring the inspecting conditions which are specified.
 7. An apparatusaccording to claim 4, wherein the control unit controls the electronbeam optics unit based on the inspecting conditions which are specified.8. An apparatus for measuring a sample with a pattern according to claim1, wherein the control unit determines an optimal number of times ofirradiation of the primary electron beam to the desired portion on thesample.
 9. An apparatus for measuring a sample with a pattern accordingto claim 1, wherein the control unit limits an irradiation of theirradiated energy of the primary electron beam to no more than 300 eV.10. An apparatus for measuring a sample with a pattern according toclaim 1, wherein the pattern is a circuit pattern formed on asemiconductor wafer, the circuit pattern including at least a porouslow-permittivity hydrogensilsesquioxane material or a materialstructurally or compositionally similar to the porous low-permittivityhydrogensilsesquioxane.